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Investments - Summarized Interest (Details) - CAD ($) $ in Millions | Nov. 25, 2020 | Apr. 12, 2019 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | --- | ---
Disclosure of subsidiaries [line items] |  |  |  |
Assets |  |  | $ 9,747 | $ 9,508
Non-controlling interests |  |  | 1,084 | 1,101
Skookumchuck |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |
Proportion of ownership interest in joint operation | 49.00% | 49.00% |  |
Skookumchuck | Entities Other Than Transalta Corporation |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |
Proportion of ownership interest in joint operation |  | 51.00% |  |
SP Skookumchuck Investment, LLC |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |
Assets |  |  | 173 |
Non-controlling interests |  |  | (88) |
Investments in associates accounted for using equity method |  |  | $ 85 | $ 0

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